1. Field of the Invention
The present invention pertains to an improved one stage process for the gasification of a carbonaceous material such as coal.
2. Description of Related Art
One of the basic processes developed for the gasification of a carbonaceous material, such as coal, is entrained bed gasification. Entrained bed gasifiers partially oxidize the carbonaceous material generating a product gas at high temperature. Thermal energy must also be recovered in order to effectively utilize the heating value of the coal. The hot product gases produced from entrained bed gasification have such high temperatures that they must be cooled or quenched prior to heat recovery in conventional heat exchangers. A further problem with entrainment gasifiers is that sticky slag particles are produced which are entrained in the hot product gases and, if not removed, tend to foul the downstream heat transfer surfaces.
U.S. Pat. Nos. 4,247,302 and 4,248,604 disclose gasification processes which utilize downflow partial oxidation reactors equipped with a diversion chamber followed by a solids separation zone to substantially remove entrained solids from the gas stream prior to passing the gas stream through one or more fire tube gas coolers.
U.S. Pat. No. 5,066,476 discloses a method of producing hydrogen rich gas which can be used for synthesis of ammonia or for hydrating of organic compounds. A hot gas from a gasifier is cooled first in a waste heat boiler, and then further cooled by adding converted circulating gas in a quenching zone. This process has the disadvantage of first cooling the hot gas containing entrained molten slag in a waste heat boiler which causes a problem with fouling of the heat transfer surfaces of the waste heat boiler and quench zone in the process. Also, this process requires expensive apparatus.
U.S. Pat. No. 4,872,886 discloses an entrained bed gasification process which attempts to solve the excessive temperature and fouling problems by use of a two-stage gasification process which allows the use of a high temperature heat recovery system including a fire tube boiler. In the first stage, the carbonaceous material, in the form of a slurry of carbonaceous material with a liquid carrier such as water, is mixed with an oxygen-containing gas and combusted. The partial combustion products are steam, slag, char and gaseous combustion products. In the second stage, a second increment of carbonaceous material in slurry form is injected into a second, unfired stage of the reactor where predominantly endothermic reactions occur. This serves to quench the hot gaseous combustion products from the first stage of the reactor and produces a nonfouling gaseous product stream that can be passed to a high temperature heat recovery system including a fire tube boiler. This patent teaches that it is essential to employ an unfired, second-stage reactor in order to avoid fouling or plugging of the fire tube boiler. Example 5 of the patent illustrates that a fire tube boiler will be plugged to inoperability in a short period of time if an unfired, second-stage reactor is not employed. Since both two-stage reactors and downflow reactors with diversion chambers are more complex and expensive than single-stage upflow reactors, it would be highly desirable to have a one stage, upflow gasification process which produces a gaseous product which could be passed directly into a high-temperature heat recovery system such as a fire tube heat exchanger without the substantial removal of entrained solids. The present invention concerns such a highly efficient one stage gasification process.